This post may seem like going back to basics but I'm constantly surprised
by the number of people who do not know, or understand,
what is written on a bottle of oil, and therefore have no idea what they
are buying/using.

To be blunt about the subject, if a bottle of oil
does not contain the following basic information then DO NOT buy it! Look
for something that does!

1) The purpose for which it is intended (i.e. Motor
oil, Gear oil etc)

3) The specifications that it meets (should contain
both API and ACEA ratings)

4) The OEM Approvals that it carries and the codes
(i.e. MB229.3, VW503.00, BMW LL01 etc)

Ignore the marketing blurb on the label - in many
cases it's meaningless and I'll explain later what statements you should
treat with some scepticism.

So, what does the above information mean and
why is it important?

THE BASICS

All oils are intended for an application and in general
are not interchangeable. You would not for example put an Automatic Transmission
Oil or a Gear Oil in your engine! It's important to know what the oil's
intended purpose is.

VISCOSITY

Most oils on the shelves today are "Multigrades",
which simply means that the oil falls into 2 viscosity grades (i.e. 10w-40
etc)

Multigrades were first developed some 50 years ago
to avoid the old routine of using a thinner oil in winter and a thicker
oil in summer.

In a 10w-40 for example the 10w bit (W = winter, not
weight or watt or anything else for that matter) simply means that the
oil must have a certain maximum viscosity/flow at low temperature. The
lower the "W" number the better the oil's cold temperature/cold
start performance.

The 40 in a 10w-40 simply means that the oil must
fall within certain viscosity limits at 100°C. This is a fixed limit
and all oils that end in 40 must achieve these limits. Once again the
lower the number, the thinner the oil: a 30 oil is thinner than a 40 oil
at 100°C etc. Your handbook will specify whether a 30, 40 or 50 etc
is required.

SPECIFICATIONS

Specifications are important as these indicate the
performance of the oil and whether they have met or passed the latest
tests, or whether the formulation is effectively obsolete or out of date.
There are two specifications that you should look for on any oil bottle
and these are API (American Petroleum Institute) and ACEA (Association
des Constructeurs Europeens d'Automobiles) all good oils should contain
both of these, and an understanding of what they mean is important.

API

This is the more basic as it is split (for passenger
cars) into two catagories. S = Petrol and C = Diesel, most oils carry
both petrol (S) and diesel (C) specifications.

The following table shows how up to date the specifications
the oil are:

SM - Introduced November 2004 - improved
oxidation resistance, deposit protection and wear protection, also better
low temperature performance over the life of the oil compared to previous
categories.

Note:

All specifications prior to SL are now obsolete and,
although suitable for some older vehicles, are more than 10 years old, and
do not provide the same level of performance or protection as the more
up to date SL and SM specifications.

DIESEL

CD - Introduced 1955 - international
standard for turbo diesel engine oils for many years, uses single cylinder
test engine only

CH4 - Introduced 1998 - development
of CG4, giving further improvements in control of soot related wear and
piston deposits, uses more comprehensive engine test program to include
low and high sulphur fuels

CI4 Introduced 2002 - developed to
meet 2004 emission standards, may be used where EGR ( exhaust gas recirculation
) systems are fitted and with fuel containing up to 0.5 % sulphur. May
be used where API CD, CE, CF4, CG4 and CH4 oils are specified.

Note:

All specifications prior to CH4 are now obsolete and,
although suitable for some older vehicles, are more than 10 years old and
do not provide the same level of performance or protection as the more
up to date CH4 & CI4 specifications.

If you want a better more up to date oil specification
then look for SL, SM, CH4, CI4

ACEA

This is the European equivalent of API (US) and is
more specific in what the performance of the oil actually is. A = Petrol,
B = Diesel and C = Catalyst compatible or low SAPS (Sulphated Ash, Phosphorus
and Sulphur).

Unlike API the ACEA specs are split into performance/application
catagories as follows:

C1-04 Petrol and light duty Diesel engines, based on A5/B5-04
low SAPS, two way catalyst compatible.C2-04 Petrol and light duty Diesel engines, based on
A5/B5-04 mid SAPS, two way catalyst compatible.C3-04 Petrol and light duty Diesel engines, based on A5/B5-04
mid SAPS, two way catalyst compatible, higher performance levels due to higher
HTHS.

Many oils mention various OEM's on the bottle, the
most common in the UK being VW, MB or BMW but do not be misled into thinking
that you are buying a top oil because of this.

Oil Companies send their oils to OEM's for approval
however some older specs are easily achieved and can be done so with the
cheapest of mineral oils. Newer specifications are always more up to date
and better quality/performance than the older ones.

Some of the older OEM specifications are listed here
and depending on the performance level of your car are best ignored if
you are looking for a quality high performance oil:

VW - 500.00, 501.00 and 505.00

Later specs like 503, 504, 506 and 507 are better
performing more up to date oils

MB - 229.1

Later specs like 229.3 and 229.5 are better performing
more up to date oils.

BMW - LL98

Later specs like LL01 and LL04 are better performing
more up to date oils.

FINALLY

Above is the most accurate guidance I can give without
going into too much depth however there is one final piece of advice regarding
the labelling.

Certain statements are made that are meaningless and
just marketing blurb, here are a few to avoid!

Recommended for use where.....

May be used where the following specifications apply.....

Approved by...........(but with no qualification)

Recommended/Approved by (some famous person, these endorsements are paid for)

Racing/Track formula (but with no supporting evidence)

Also be wary of statements like "synthetic blend"
if you are looking for a fully synthetic oil as this will merely be a
semi-synthetic.

Like everything in life, you get what you pay for
and the cheaper the oil the cheaper the ingredients and lower the performance
levels.

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